I recently lost 20lbs in one month. I did a 1200 calories diet, no flour, rice, bread. I also use artificial sugar and drank only water. No soda, juice, milk, only green juice that I made.
So basically I ate greens, grilled meat, chicken, and fish.
So far I have been able to maintain that weight lost. I continue to use artificial sugar and limited things with added sugar.
I have three beachbody programs and while there are good, I have never lost so much as I did with this diet.
I believe that you have to control your diet before added exercise.